A backlight unit is for providing a light source for display devices such as Liquid Crystal Displays (LCDs). As a LCD does not emit light itself, a light guide plate (LGP) is an important component of the backlight unit and functions to transform a line light source to a surface light source.
Conventional LGPs are made of materials such as Polymethylmethacrylate (PMMA), Polycarbonate (PC), Styrene methyl methacrylate (MS) resin and Polystyrene (PS). The physical property, specifically the density and melting point, of the materials are respectively: PMMA, 1.15 g/cm3 and 160° C.; PC, 1.22 g/cm3 and 220° C.; MS, 1.12 g/cm3 and 160° C.; PS, 1.05 g/cm3 and 180° C. A convention edge-lit LGP 01 has a working state as illustrated in FIG. 1, in which a plurality of Light Emitting Diode (LED) 02 functions as the light source. Due to the limitation of the emission angle (a normal LED has an emission angle of about 120°), a triangular dark region 03 exists between two neighboring LEDs in which no light can reach. If the brightness of the dark region is too low, hotspots will occur, which would affect the picture quality.
The currently available solutions for the hotspot issue have obvious disadvantages. For example, a pitch between two neighboring LEDs may be adjusted by design to decrease the dark region. However, more LEDs will be needed when the distance between LEDs is decreased, which will increase the cost. The hotspot phenomenon may be alleviated by adjusting the brightness of the dark region through designing the pattern of the LGP, which can mitigate the hotspot but is difficult to realize. The hotspot phenomenon may also be solved by replacing the existing film material with a better film material, which will increase the cost.